12 F350 trans question

Currently on a 5 hour haul in step dad's truck. He has it on cruise and every so often it has a shimmy in the transmission like it wants to shift. But it isn't changing gears, just a hiccup so to speak, like it wants to downshift. He said it started about 2 weeks or so ago. So he had it serviced for about $250 last week.

Any thoughts on a cause?

E: 6.7L with 102K miles. doesnt seem to do it when not in cruise control